|Other Abstract||Lignin, the second most abundant biopolymer on earth, is one of renewable natural biomass resources. In China, industrial lignin mainly existed in the waste liquor from the paper and pulping industry has the properties of rich sources, low price and poor water solubility. Using industrial lignin as raw material, producing environmentally friendly green fine chemical products via chemical modification and developing green chemical processes not only reduce the pollution damage to the environment caused by the pulping waste liquor, but also increase the economic value added of industrial lignin, which has double significance in environment and resource.
Firstly, lignin carboxylic acid derivatives (LCA) has been prepared by oxidation of lignin by dilute HNO3 and NaNO2 under mild conditions. In order to introduce a large number of hydrophilic carboxylic acid groups, the alcohol hydroxyl groups in the side of alkaline lignin were oxided to carboxylic acid without damaging the main structure of lignin. The results show that the lignin-based carboxylic acid was produced under the optimum conditions of nitric acid and lignin with mole ratio 8:1(the acid concentration is less than 1mol/L), nitrite and lignin with mole ratio 10:8, reaction time of 24h, reaction temperature of 20℃. The structure and properties of lignin-based lignin-based carboxylic acid has been characterized by elemental analysis , FT-IR, GPC, NMR and Boehm titration. The results show that in the lignin carboxylic acid derivatives, the carboxylic acid content is 3.4mmol/g, and the total acidic groups reach 4.1 mmol/g. Furthermore, the main frame structure of lignin molecule has been preserved in the process of synthesis.
The adsorption performances of heavy metals (Cr(III), Cu(II), Pb(II) and Cd(II)) onto LCA have been investigated. The effects of pH, concentration of heavy metal ions, and contact time on adsorption have been studied using batch experiments. The results suggest that the adsorption behavior of metal ions on LCA is dependent on the above three factors. Langmuir and Freundlich models were applied to describe the adsorption of metal ions on LCA. Langmuir and Freundlich isotherms exhibit good fit to the experimental adsorption data, and the maximum adsorption capacities of LCA for the four metals are in the following order: Cd(II) >Pb(II) >Cr(III)≫Cu(II). Moreover, the metal-loaded LCR can be easily regenerated and reused by a simple acid treatment with the desorption efficieny above 95%.
Secondly, for resource utilization of the used adsorbent, the Fe-loaded lignin carboxylic acid are used as the raw materials for preparation of lignin-based magnetic carbon (LMC) by calcination method, developing the new route of value-added utilization of lignin. The effect of Fe2+ concentration, immersion time, calcining temperature, and calcining time on the structure and catalytic activity of LMC has been investigated. The results showed that optimal conditions for preparation of LMC were: Fe2+ concentration 107 mmol/L, impregnation time 4 h, calcination temperature 900 ℃, calcination time 2 h. The surface morphology and phase composition of LMC were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS). The results show that the calcination temperature and calcination time have the important effect on the catalytic activity of LMC , and there are many kinds of iron oxides in the LMC microporous materials, such as FeO, Fe2O3, Fe3O4 and FeOOH. LMC can be used as a heterogeneous Fenton catalysts for catalytic degradation of dyeing wastewater.
The catalytic degradation of the simulated dye wastewater of RhB has been studied used LMC as heterogeneous catalyst, and the effect of pH, LMC dosage, H2O2 concentration and dye concentration has been investigated. The results show that the suitable degradation conditions for the dyeing wastewater were pH value 3, catalyst concentration 1 g/L, hydrogen peroxide concentration 8.56 mmol/L, RhB solution initial concentration 100 mg/L. The degradation rate of RhB is nearly 100% within 15 minutes under these optimal conditions. The recyclability of LMC catalyst was also tested. Only slightly decrease in activity was observed after the catalyst was recycled five times, and the dissolved iron ion concentration in aqueous solution was lower than pollutant emission limit value for industrial wastewater in EU, indicating that LMC can function as a stable catalyst.|